1. Field of the Invention
The present invention relates to a wireless communications protocol. More specifically, the present invention discloses a data discard signalling procedure.
2. Description of the Prior Art
In a wireless communication system, a protocol data unit (PDU), which contains a segment of a service data unit (SDU), may be transmitted and retransmitted for a maximum number of transmissions without positive acknowledgement from the peer receiver. To control the transmission window of the sender, a state variable VT(A) is defined to be the sequence number (SN) following the SN of the last in-sequence acknowledged PDU. Alternatively, to control the reception window of the receiver, a state variable VR(R) is defined to be the SN following the SN of the last in-sequence PDU received. Another state variable, VR(H), is defined to be the SN following the highest SN of any received PDU. A data (SDU) may be transmitted and retransmitted within a predefined duration of time. After a time out period or after the number of transmissions has reached a maximum number, the SDU is deemed out-of-date and is discarded by the transmitter. For acknowledged mode (AM) transmission, the transmitter needs to signal the receiver of the discard of the SDU so that the receiver can move its reception window accordingly. This signalling procedure is called an SDU discard with explicit signalling procedure. Refer to FIG. 1 which illustrates the procedure.
A move receiving window (MRW) super-field 120 is utilized to request the receiver 110 to move its reception window and optionally to indicate the set of discarded Radio Link Control (RLC) SDUs, as a result of an RLC SDU discard in the Sender 100. The receiver 110 responds with an acknowledge signal 130.
However, in certain situations, the SDU discard with explicit signalling procedure will not be terminated. In these situations the receiver 110 has moved its reception window to a position which is exactly what the sender 100 wanted to signal to the receiver 110. If the procedure is not terminated when this criterion is fulfilled, the sender 100 must retransmit MRW SUFI 120 when an MRW timer expires. This will waste radio resources and slow down the transmission throughput.
Furthermore, if the number of transmissions of MRW SUFI 120 reaches its maximum value when this criterion is fulfilled, the RLC entity will unnecessarily reset itself. This results in a degradation of transmission performance.
Therefore, there is a need for a more efficient data discard signalling procedure that improves transmission throughput and performance.